1. Field of the Invention
The present invention relates to an apparatus and a method for cutting a hollow cylindrical workpiece of metal with a laser beam to produce a plurality of metal rings.
2. Description of the Related Art
Some power transmitting belts for use in continuously variable transmissions for automobiles are in the form of a laminated ring belt comprising a stack of metal rings. For example, as shown in Japanese Laid-Open Patent Publication No. 2005-297074, the metal rings of the laminated ring belt are produced by joining the opposite ends of a rectangular thin sheet of metal to form a hollow cylindrical drum (hollow cylindrical workpiece) and then slicing the drum into a plurality of metal rings each having a predetermined width.
It has heretofore been customary to slice the drum with a cutter such as a grinding wheel, a cutting tool, or the like. Attempts have also been made to use a laser beam to cut a hollow cylindrical drum as disclosed in Japanese Patent Publication No. 63-053912 and Japanese Laid-Open Utility Model Publication No. 59-062879.
When the drum is cut by the laser beam, the temperature of the drum rises due to the laser beam applied to the drum. Since the laser beam is relatively high in temperature, the temperature of the drum tends to increase even at those positions which are relatively spaced from the position where the laser beam is applied to the drum, occasionally to such a degree that the heated regions melt away.
After the laser beam stops being applied, the molten regions are solidified again into a mass referred to as dross. The drum thus takes a shape having raised regions due to the dross. The metal rings that are cut from the drum with the raised regions cannot properly be stacked one on another because the dross is kept in physical interference with and pressed against the metal rings.
To alleviate the above drawback, the metal rings may be machined to remove the dross in a subsequent machining process. However, since the subsequent machining process adds to man-hours required to produce desired metal rings, the efficiency with which to manufacture the laminated ring belt is lowered.